Hi Speedyman41:
I don't know how, but probably some of the things I did yesterday
worked because I rebooted the computer (without knowing that that was
to reboot it), and when I opened it again in the night my beloved
volume icon appeared there, in its place again! :D . So, thanks anyway,
I guess that all the info I got from this site worked at the end of the
day, although I don't know exactly what was that was needed to be
done... ;)
Take care
Beatriz